TEXTILE

TEXTILE PROCESSING : Fibre production

Cotton is cultivated as a shrubby annual in temperate climates but can be found as a perennial in tree-like plants in tropical climates. The cultivated shrub grows from about one to two metres tall over a growing period of six to seven months.

Warm and humid climates with sandy soil are the most suitable. Although cottton can be grown between latitudes 45oN and 30oS, yield and fibre quality are considerably influenced by climatic conditions, and best qualities are obtained with high moisture levels resulting from rainfall or irrigation during the growing season and a dry, warm season during the picking period. Rain or strong wind may cause damage to the opened bolls. Cotton producing areas vary in climate from arid to semi-humid. Some of the biggest include parts of the USA, China, Russia, Brazil, Mexico, Egypt, Sudan, Turkey and India. African producers include the Ivory Coast, Nigeria, Uganda and Tanzania.

Every year, new seed is planted, the crop grown to maturity, the seeds with their fibres harvested, the dead plants destroyed and the land prepared for the following season. The lint or raw cotton, is shipped to textile factories all over the world, while most of the seed is processed for its food components (soaps, margarine and animal feed cake). Only a small quantity of seed is retained for planting.

Cotton is a key agricultural product in the world’s economy, and is particularly important to developing countries. Production in the Third World provides a livelihood to 125 million people. It ensures that developing countries have an important source of foreign exchange ($25 billion annually) and a major raw material to develop their own textile industries.

Cotton needs a lot of water to grow, over 50cm of rain in a season. However, cotton can be grown with less rainfall by applying supplementary water from irrigation channels.

Pests in the cotton can be controlled by the regular application of pesticides sprayed onto the plants. Cotton is attacked by several hundred species of insects. Limited insect control can be achieved by proper timing of planting, or by selective breeding of varieties with some resistance to insect damage. Chemical insecticides, which were first introduced in the early 1900’s, require careful and selective use because of ecological considerations but appear to be the most effective and efficient means of control.

Cotton plants are also subject to diseases caused by fungi, bacteria and viruses. The treatment of seeds before planting is common, as is the practice of soil fumigation.

A really good field of cotton ready for picking will yield about 1000 kg of cotton fibre per hectare. Yields vary, but the present world average of only 400 kg per hectare could be improved. Crops could be increased without using any more land in developing countries if agricultural knowledge could be applied and supplies of pesticide and fertiliser made available to the farmers there. Even in the more advanced countries, the improvements in seed varieties and farming techniques give better yields per hectare almost every year. The present world production of cotton is about 13 million metric tonnes which is grown on about 32 million hectares.

On small farms cotton is hand picked. It is packed in loose bales and is marketed by farmers at local seed cotton markets. The buyer then provides the transport to national ginneries. In countries where labour costs are high and where the terrain is suitable, machine picking is used. These machines collect immature bolls and other vegetable matter, which is called trash. To minimise the trash collected, the plants are sometimes sprayed with a chemical defoliant causing the leaves to drop prior to picking.

Ginning machines are designed to separate the cotton fibres from the seed. The separation of fibres from seed is effected by means of a row of circular saws passing through a series of narrow grids. The saw teeth grip the fibres and draw them through the grids. The seed is too wide to pass through and the fibre is thus pulled from the seeds.

Cotton is then baled in loads of 220kg. The bale which is fabric or plastic covered is secured by strong metal bands.

Wool is available in a wide range of fineness, crimp, length and colour. Types are denoted by quality numbers on a subjective scale related to fineness, spinnability, etc. Merino wool is usually about 60’s –64’s, crossbred wool is 48’s-60’s.

There are about 1000 million sheep of nearly 500 different breeds scattered about the world, with large concentrations in New Zealand, Australia, South Africa, South America, China and Russia. The British share of the world’s sheep is 3%, with a 2% share of the world’s wool, but British sheep have made contributions to the world’s flocks out of all proportion to the story the statistics alone tell.

In order to protect the sheep during its productive lifetime, regular treatment with pesticides is given in the form of a sheep dip. These pesticides, some of which are organo-phosphorus, can be harmful to humans and so great care must be taken when the sheep are being treated. Residual pesticides also find their way into surface and ground water supplies and are found in the waste liquors from raw wool scouring.

The basic steps in wool processing have remained unchanged for centuries. Wool obtained from different parts of the sheep varies in fibre fineness, length and crimp. There are variations between locks, or cohering bunches of wool, and between fleece from different areas of the sheep. The quality of wool obtained from the belly is short and burry; the shoulders yield the finest wool. Sorting is the separation of the different qualities of wool from the fleece. The most important property is usually fibre fineness, closely related to softness of handle. The sorter unrolls the fleece on the sorters board, usually waist high, and cuts away any wool carrying tar or paint marks. He next removes the coarsest wool, placing it in a separate basket, and finally reaches the fine wool on the shoulders. A sorter can generally sort up to 4500 kgs of Australian fleece in a week.

Flax requires a temperate climate free from heavy rains and frosts. Frequent moist winds during the growing season are advantageous. Hot dry summers produce a short and harsh but strong fibre; moderately moist summers produce plants yielding fine, strong, silky linen.

Flax is difficult to grow because of the soil preparation required before sowing, and the heavy applications of artificial fertilisers required. After a slow initial growth, the plants grow as rapidly as one inch per day for 30 to 40 days. Blossoms then begin to develop and stem growth ceases. Flax is normally a three month crop, although this growing time varies with climatic and other growing conditions.

It is attacked by several fungal and viral diseases, usually kept under control by chemical treatments of the seed, or by cultivation of resistant varieties. Harvesting is usually carried out by pulling the plant from the ground. Pulling is considered superior to cutting since flax deteriorates at the cut. Yields of fibre per acre vary from 200 to 360 kgs.

Like other bast fibres, flax must be separated from the stalks by retting. Water retting, which is essentially bacterial, is practised in areas such as the Philippines, Taiwan and China; most of the crop grown in Russia and the United States is dew retted, which is predominantly fungal. In this method the harvested flax straw is left in the field and allowed to remain until the combined action of the moisture from dew and micro-organisms makes separation of the fibres possible. The process depends very much on the temperature and chemical nature of the water, but takes only six to eight days under controlled temperature conditions. After removal of the stalks from the retting medium, thorough drying is necessary to prevent further fermentation.

The retted and dried fibres are removed from the woody remainder of the stem by the process of scutching, in which the stems are first broken by passage through a series of fluted metal rollers, and the fine pieces of the woody portion of the straw, called shives, are beaten out. About a tenth of the original flax stem is useful fibre.

Although the lifecycle of Bombyx mori is typical of most other silkmoth species, domestication over the ages has deprived the moth of its ability to fly. This feature is exploited in sericulture to introduce an orderly sequence into the whole cycle, for the moths can be put in desired places for egg laying.

The fully grown silkworm has two silk glands each filled with a concentrated solution of the silk proteins, fibroin and sericin, the latter forming a sheath around the former. The two glands unite in the spinneret, a minute aperture in the muzzle of the worm.

Immediately prior to the process of pupation the worm first attaches silk fibre to various supports, to form a scaffolding, and then extrudes the silk thread and deposits it layer upon layer to form a cocoon around itself. Most cocoons, except those required for propagation purposes, are subsequently heated by a process known as stifling to kill the chrysalis within and prevent the emergence of the moth which otherwise would make the cocoon unreelable. Following the stifling process the cocoons are inspected and graded, defective ones are separated for subsequent treatment as silk waste.

Reeling consists of unwinding the fibre from several cocoons together and reeling the baves so as to form a composite thread of the required denier. A Bombyx silk bave is only about 15 to 25 microns thick and it is too thin and weak to be used singly. The reeling process consists essentially of softening the silk gum, by maceration in hot water, removing the loose outer layers until the free end of the bave has been located and then combining it with the baves from other cocoons.

Although much of the world’s silk is still reeled from hand operated basins, 99% of the silk produced in Japan (the world’s largest producer and consumer) is reeled on automatic reeling machines. With these machines the process is considerably less labour intensive.

Silk throwing involves the preparation of the raw silk into a form suitable for knitting and weaving. The first process is that of soaking the hanks in a warm emulsion of various oils and other softening agents in a slightly alkaline solution. During this process the oils are taken up by the silk gum. The objective is to make the yarns more supple and pliable. Following soaking and drying the hanks are rewound on to bobbins or cones. It is at this stage that twist is inserted to form different types of yarn.

Many silk fabrics are still produced on hand looms which can produce superior goods for which the purchaser is obviously prepared to pay the extra cost involved.

Some 60% of the silk extruded by the silkworm is useless for the production of continuous filament yarns, and the spun silk process is based on the utilisation of this material. The technique of spun silk production is quite distinct from that of thrown silk yarns, and many of the mechanisms involved in the process are closely related to machines used in the preparation and production of yarns from staple fibres such as cotton, wool, flax and jute. After degumming, cleaning and opening, the fibres are cut into short lengths and then combed into slivers. These are made into yarns by mixing, drafting and spinning.

The basic method of viscose fibre production can be split into five stages. Firstly, sheets of cellulose in the form of purified wood pulp are steeped in caustic soda solution and then pressed to remove the excess and ground into crumbs. The crumbs are allowed to stand for a time during which ‘ageing’ occurs, the very long cellulose molecules are thus reduced in length to allow a satisfactory spinning solution to be prepared later.

The product ‘alkali cellulose’, is churned with the liquid carbon disulphide to form a soluble derivative of cellulose, cellulose xanthate. The crumbs turn orange in colour and are then dissolved in a second caustic soda solution forming the syrupy liquid viscose.

The viscose is allowed to stand for a controlled time to ‘ripen’. The chemical and physical character of the solution changes slowly with time until an optimum spinning condition is reached. Meanwhile it is subjected to vacuum to remove gas bubbles and filtered.

The viscose is extruded at a measured rate through the holes of spinnerets that are immersed in a bath containing water, sulphuric acid and salts. The emerging filaments are coagulated and chemically changed back to cellulose. They are drawn from the bath at a controlled rate that involves some stretch, and collected.

Either continuously or in batches, the fibres are washed free of coagulating bath chemicals, are treated with further chemicals and are finally washed, lightly oiled, and dried. In its final form the fibre may be either continuous filament or cut staple.

Viscose – Viscose fibres together with acetate fibres represent man-made fibres made from cellulosic (wood pulp) sources. These fibres were developed around 1900.

There are two other man-made regenerated fibres, namely cuprammonium and modal (polynosic).

Standard-type viscose fibres have moderate strength and are relatively stiff compared with fibres such as cellulose acetate and nylon. Strength is reduced in wet conditions, so that heavy duty end uses would not be expected. Viscose is a limp handling fibre because its polymer system is so very amorphous. Its polymers are not sufficiently long for a more satisfactory alignment, and so do not allow the formation of more hydrogen bonds which would result in a more rigid polymer system and thus a crisper handle to the fibre and textile.

The very amorphous polymer system of viscose, as well as its polar polymers, make viscose the most absorbent fibre in common use. The slightly more crystalline polynosic rayon is somewhat less absorbent than viscose. As would be expected, viscose and the other regenerated cellulosics have somewhat similar thermal and chemical properties to cotton. However, the shorter polymers and the very amorphous nature of regenerated fibres are responsible for their much greater sensitivity to acids, alkalis, bleaches, sunlight and the weather.

Whereas all fibre making processes are governed largely by their inherent costs and the utility of the product, three additional factors assume great importance; raw material supply, energy requirements, and environmental impact of the production process. The use of raw material, wood pulp, in the viscose process means that a renewable resource is involved, and this is produced from softwoods growing in northern latitudes on land unusable for other forms of agriculture, or from hardwoods growing at a phenomenal rate in sub-tropical areas. The production time of 10 to 20 years for wood compares with 100 million years for the non-renewable fossil fuels such as oil used as feedstock for synthetic polymer production. Further, the use of wood pulp for the viscose process is only a small fraction of total pulp usage, and in general pulp production keeps up with demand. Other materials required for the viscose process are caustic soda, sulphur chemicals and salts, and these are in abundant supply.

The considerable pollution of air, watercourses, and land associated with older viscose plants, and current health fears over carbon disulphide air pollution, have been significant problems. Technological advances are however, making possible complete recovery and recycling of many chemical materials used in the process.

In general, the status and prospects for continuous filament viscose have declined and there were many plant closures in the 1970’s. However, the fact that the source of raw material is renewable, and the desirable properties of the product in which comfort and moisture are prominent, point to a more promising future. Problems with relatively high energy costs and high manpower requirements are still being investigated to ensure investment in viscose plant.

The raw material for the production of polyester is oil. In the first step of production the oil is cracked to give ethylene gas. This is oxidised in air with a catalyst to form ethylene oxide, which is then hydrated to produce ethylene glycol. This process was already well established for the production of antifreeze and explosives, but a new commercial process had to be developed for the other component, terephthalic acid. This is made from para-xylene, which is distilled from petroleum and then highly purified.

Either the acid or its ester, dimethyl terephthalate, is added to the ethylene glycol and then polymerised in a vacuum at a temperature of about 270C. The polymer is extruded from the polymerisation vessel in the form of a ribbon which, after cooling, is cut into chips ready for further processing.

The bulk polyester is formed into filaments or fibre by first drying and then melting the chips, and then pumping the molten polymer through many holes in a spinneret. The fine filaments solidify quickly and are wound up either at a speed of about 1000 m/min to produce undrawn yarn, or at about 3500 m/min to produce a partially orientated yarn.

The nylon developed at Du Pont is formed by thermal polycondensation of hexamethylene diamine and adipic acid, each component having six carbon atoms, hence the name nylon 6.6. The first part of the process consists of mixing the two components in exact proportions in methanolic solution from which the nylon salt settles out. A concentrated solution of this salt is first heated under pressure in an inert atmosphere to about 270C; steam is then bled off and the residue is heated further under vacuum to complete the polymerisation.

The nylon developed at IG Farbenindustrie is made by thermal polymerisation of caprolactam in an inert atmosphere at temperatures up to 270C, followed by the extraction with water of about 10% residual monomer before the polymer can be used. As the repeating unit in the polymer contains 6 carbon atoms it is called nylon 6.

Nylons are thermoplastic, i.e. they progressively soften on heating and eventually melt, nylon 6 at 210C and nylon 6.6 at 250C. This enables them to be extruded in their molten state through small holes in a plate called a spinneret to form very fine jets of molten polymer that quickly solidify to continuous filaments as they are transported down a cooling chimney to the wind-up positions.

The basic material for acrylic fibre production is acrylonitrile. This is usually produced by the so called Sohio process.

Before 1960, acrylonitrile was commercially produced by adding hydrogen cyanide to acetylene, or by dehydration of ethylene cyanohydrin. The discovery and development of the ammoxidation of polypropylene (Sohio process), appreciably reduced production costs because of the lower cost of raw materials and the single step nature of the process. In the Sohio process, propylene, ammonia, and oxygen, react at high temperature in the presence of catalysts such as bismuth phosphomolybdate.

The acrylonitrile monomer is then combined with other monomers to produce co-polymers or polymerised alone to form homopolymer acrylic. In order to qualify for the description acrylic, the final polymer must contain at least 85% by weight of acrylonitrile units. Acrylonitrile is an addition polymer, the monomers adding or joining end-to-end without liberating any by-product.

Although acrylic polymer is thermoplastic, it does not melt sharply to give a fluid melt suitable for melt spinning, and so must be solvent spun. This fact delayed development of the fibre while a suitable solvent was found. Typical solvents include dimethylformamide, dimethylacetamide, dimethyl sulphoxide, ethylene carbonate, sodium thiocyanate (50% in water), zinc chloride (60% in water), and nitric acid (70% in water).

Acrylic fibres are either wet or dry spun.

Principal pollutants: Emissions from oil processing, carbon disulphide from viscose production, fertilisers in cotton and flax growing, pesticides in cotton, flax and wool production, methane (from sheep rearing), emissions from the transportation (fuel usage) of fibre.

TEXTILE PROCESSING : Fiber to Fabric

Spinning (includes; opening, carding, combing/drawing, roving, spinning and winding).
The fibre contained in cotton bales, for example, is first opened and cleaned. The trash is removed and a lap or sheet of fibre is produced. Selection of layers of cotton from different bales allows fibre blending to take place at this early stage. Material losses can be 5% or more. Carding converts the lap to a parallel sliver, removing more of the trash and some lint. In some modern systems, tufts are fed through tubes directly to the card. The carding action takes place between the surfaces of a large cylinder and a system of overhead revolving flats, which are covered with fine wire points. This process produces about another 4% to % in waste. The fibres collected at the end of the card in the form of a filmy web, are condensed into a card sliver of about 25mm diameter. The sliver is then delivered into a tall can. Combing, the next process (although optional, depending on the end use of the yarn), removes short fibres and any remaining trash or nep. A lap forming machine is used to combine a number of slivers into a wide ribbon of fibre which is then presented to the comber. The total material loss up to this stage can be as much as 15%, depending on the grade of cotton. In drawing, the card sliver is drafted down to an intermediate roving. It is at this stage that man-made fibres are blended into the final roving. At the speedframe a single drawframe sliver is drafted 5 to 10 times and a slight twist added. This is wound onto a roving bobbin. The roving is then spun into yarn. Total losses from fibre to yarn can be large. For example 100 kgs of 50/50 polyester cotton yarn can require 56 kgs of polyester and up to 70 kgs of cotton.

In ring spinning a fine sliver of fibres is fed downwards from a roving bobbin through a drafting zone, which drafts out the strand of fibres to the correct thickness. The yarn is then wound onto a second package called a ring bobbin. Twist is then inserted by the combined action of the spindle and the traveller. The ringframe, in one form of another, is used for spinning all types of staple fibre, wool, cotton and synthetics.

Ring Spinning
Another more recent method of yarn formation is called rotor spinning. This is a form of open-end spinning where twist is introduced into the yarn without the need for package rotation. Allowing for higher twisting speeds with a relatively low power cost. In rotor spinning a continuous supply of fibres is delivered from delivery rollers off a drafting system or from an opening unit. The fibres are sucked down a delivery tube and deposited in the groove of the rotor as a continuous ring of fibre. The fibre layer is stripped off the rotor groove and the resultant yarn wound onto a package. The twist in the yarn being determined by the ratio of the rotational speed of the rotor and the linear speed of the yarn. The use of this system has two basic advantages. It is fed by sliver, not as with the ringframe by roving, and so eliminates the speedframe from the process line. It can also be modified to remove any remaining trash, thereby improving the yarn quality.
Open-end spinning produces a different type of yarn to ringframe spinning. Open-end yarns tend to be more uniform, lower in strength, more extensible, bulkier, more abrasion resistant and more absorbent. It is likely then with all of these differences, only some of which are beneficial, that open-end spinning will not replace ringspun yarn as originally thought, but will be a complimentary product.

Rotor Spinning
The production of worsted or woollen yarn differs from cotton in that the raw loose fibre is first scoured, washed, dried and blended. Carding and condensing for woollens and carding, gilling, combing (Noble or French), gilling again, blending and drawing for worsteds. The result is what is called a white wool top. The top is then drawn and spun into yarn. Woollen yarns are made up of fairly short fibres, loosely spun with little twist. Worsted yarns however, are made up of longer fibres with a higher twist. Woollen yarns have a fuzzy appearance whilst worsted yarns are smooth.

Typically about 40 to 60% of the original raw wool is made up of wool grease, suint (water soluble wool wax), excess water and dirt, which is removed on scouring and drying. Oil is then added prior to carding to reduce later breakages. A further 1 to 4% waste consists of burr which is removed at the carding stage (alternatively it can be removed by carbonising which is an acid treatment process).

Twist is inserted into the yarn at the spinning stage. If the direction of the twist is to the left, looking up the thread, it is called S-twist. If to the right it is Z-twist. When yarn is made of one strand of twisted fibres it is known as a singles yarn, and when two or three singles are twisted together it is a twofold or threefold yarn. When folded yarns are twisted together the result is a cabled yarn. There are also a range of what are called ‘fancy yarns’ which are obtained by variations in how yarns are twisted together. These include slub, loop and gimp yarns.

Principal pollutants: noise and dust.

Typical noise levels found near carding machines, 84 dB(A); combing machines, 90 dB(A); in twisting and texturing rooms, 101 dB(A); ring spinning rooms, 92 dB(A); open end spinning, 93 dB(A); automatic cone winding rooms, 93 dB(A).

Typical total dust levels found around these processes (opening to spinning) vary from 0.1 to 2.5 mg/m³. With the higher levels found around opening and carding machines. Levels depend on the type of yarn processed, air ventilation rates and the age/ type of machine used.

Weaving ( includes; beaming, warp sizing and fabric/carpet weaving).
Before weaving can commence the warp yarns must be assembled onto a beam. At this stage, cotton and some man-made warp yarns are sized to improve their strength and to minimise breakages. The size is squeezed into the threads as they pass between rollers and drying is achieved by large steam heated cylinders. A variety of substances can be used as size, but typically these are either polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose or starch.

Warp Sizing
The yarn is now ready to be woven into fabric. A number of different types of loom are available for this process, conventional shuttle, gripper shuttles, rapier, multi-phase, air jet or water jet. Although, conventional shuttle looms have now been replaced to a great extent by shuttleless rapier looms.

The Jacquard loom is different in that it is used for weaving elaborate fabrics such as curtains and upholstery. Instead of the usual arrangement of healds the jacquard is equipped with a series of cords and attachments called a harness. This enables each warp thread in each repeat of the pattern to be lifted independently. Movement of the harness is controlled by perforated cards threaded together into an endless loop, in which the punched holes correspond to the pattern.

Typical weave structures are calico or plain weave; twill weave, which produces diagonal lines in the fabric; sateen weave, which is predominantly weft-faced with a smooth surface; and figured patterns made on a Jacquard loom.

A carpet is essentially a heavy pile fabric with vertical tufts or loops held in place with a backing material. Carpet can be constructed by weaving the pile and backing simultaneously, or by punching the pile loops into an already prepared woven backing. The latter is called a tufted carpet and these tend to be constructed using a nylon pile and jute or polypropylene backing. A secondary backing with latex foam may also be applied on the cheaper tufted carpets.

The more expensive woven carpets such as Wilton and Axminster are woven on large carpet looms, some controlled by a jacquard system, not unlike the ones used for fabric patterning. Most Wilton type carpets are woven face to face and then split down the middle to form two carpet pieces. Woven carpets are generally made of a wool/nylon blend of fibres with a jute backing.

Principal pollutants: noise, dust and high effluent COD from residual sizing liquor.

Typical noise levels found in shuttle loom weaving rooms, 100 dB(A); gripper shuttle loom weaving rooms, 95 dB(A); rapier looms 92 dB(A).

Typical total dust levels found in weaving sheds vary from 0.1 to 6.0 mg/m³. Levels depend on the type of fabric processed, air ventilation rates and the type of loom used.

Knitting (includes; texturing, winding, warping and knitting).
Man-made yarn is textured by twisting the yarn and heat setting it into place before cooling and untwisting. On relaxing the yarn has a bulky, elastic property suitable for knitted fabrics. Air texturing, an alternative process, uses high velocity air instead of heat. The yarn is then wound onto cones.

Knitted fabrics are made by interlacing loops of yarn. Weft knitting is when successive loops of a single yarn form a row running across the width of the fabric. Warp knitting is when successive loops of yarn run along the length of the fabric. Weft knitting produces a more extensible fabric and tends to be used for producing items such as stockings, tights and socks.

Knitting machines are either circular or flat bed. There are many types of circular knitting machines. A single jersey type utilises one set of needles for knitting, disposed around the circumference of the machine. Yarns are fed in from numerous bobbins in creels at each side of the machine and delivered to the needles at various feeder points around the circumference. Cloth produced by this method is tubular and is collected on a cloth roller at the base of the machine. Another type of knitting machine is the flat V-bed type which uses a single yarn supply which moves backwards and forwards on a carriage. Fabric produced by this machine is flat, rather than tubular, and is usually employed for making heavier fabrics suitable for garment blanks for pullovers and cardigans.

Raschel or tricot warp-knitting machines are used for knitting coarse and fine gauge fabrics. Coarse gauge raschel is used for outerwear, furnishings and industrial purposes, whilst fine gauge tricot is used for lingerie, sheets and shirts.

Warp knitting is also used in the production of lace, net and elasticated net (which used as a backing or lining material for stretch garments).

Circular Weft Knitting Machine

Principal pollutants: noise and dust.

Typical noise levels found in a warp knitting room (compound needles) 92 dB(A).

Typical total dust levels found in knitting rooms vary from 0.2 to 1.2 mg/m³.

Non-wovens (includes; needlepunching, adhesive bonding, stitch bonding, spun bonding, spun laced and wet laid).
Needlepunching, the first of six methods used to form a non-woven, produces an interlocking of the fibres in a fleece. The fleece is usually derived from a carding machine. The action of the needles pushes some of the fibres down through the fleece effectively holding it together. In adhesive bonding, adhesive is impregnated or sprayed onto the fleece. It is then dried in an oven. Stitch bonding is a process by which the fleece is held together by a knitted structure based on interlooping tufts of fibre from the fleece. Spun-bonded materials are based on a continuous filament being randomly deposited onto a porous belt with suction. The web is then heated or chemically bound, producing a more traditionally textile-like non-woven fabric. Spun lacing is similar to needle punching but uses a high velocity jet of air instead of a needle, whilst wet laid, a process with limited success, is very similar to the paper making process.

Principal pollutants: Noise (to a lesser degree than spinning, weaving and knitting)

Typical noise levels in adhesive bonding are 83 dB(A), whilst in needle punching, levels are about 85 to 86 dB(A).

Preparative Treatments

Singeing
Cotton is prepared for dyeing by removing the surface fibres. This is done by singeing the surface of the fabric with a gas flame. The equipment used for this process is very simple and has changed little in design over the years. Both flat and tubular knitted fabrics as well as woven fabrics can be singed. Desizing units are sometimes used in conjunction with the singeing process.

Principal pollutants: dust and fume.

Typically levels of dust in the process emissions from singeing are of the order of 10 to 40 mg/m³, whilst in the workroom levels vary from 2 to 30 mg/m³.

Desizing
The size added to the yarn prior to weaving must now be removed. This is achieved by either an enzyme treatment or by dilute acid and a simple washing off procedure. If starch is the size on the fabric then it can contribute up to 50% of the total BOD loading from the processing of a typical woven fabric. Other sizes such as PVA are recoverable and so have less of an impact on effluent BOD.

Principal pollutants: High BOD/COD in effluent.

The chemical oxygen demand (COD) of a desizing effluent varies between mg/l and mg/l. Water usage for this process is of the order of litres per kg of textile.

Scouring (including; loose stock, yarn, fabric scouring and milling)
Scouring of cotton or man-made fibres to remove oils or lubricants, is done at either the hank, yarn or fabric stage, prior to dyeing. This is not the case for wool, where the large quantity of impurities present means that it is always necessary to scour the fibre in its raw state. Cotton and flax scouring is usually done at high temperature using a caustic liquor, whilst wool goods require a milder soap and soda, or detergent scour at low temperature. Raw wool scouring, washing and drying is usually done in a single continuous operation prior to blending.

The milling of woollen fabrics is a process, which effectively compacts the textile structure producing a change in handle from a slight to a dense matting or felting. The process is undertaken at low temperature using soap and soda or detergent. The process was originally undertaken on old open topped wooden milling machines, some of which are still in use because of their gentleness in processing and hence better fabric finish that they can provide. More modern milling machines resemble winches in shape and basic design, they may not be as gentle as the old machines, but they can be used for a wider range of processing.

Traditional Raw Wool Scouring

Principal pollutants: High effluent BOD (biochemical oxygen demand)/COD and solids. Pentachlorophenol residues from cotton scouring and pesticide residues from wool scouring .

Wool scouring effluent has a pH of between 8-10, with a COD of between 5000 and 35000 mg/l and a suspended solids content of anything up to 20000 mg/l. Cotton scouring effluent and wool milling effluent are considerably less polluting with respective COD’s of about mg/l and mg/l and suspended solids contents of mg/l and mg/l.

Severe limitations are placed on the concentration of PCP and pesticides in textile effluent. The cost of treating effluent containing these substances is usually high. The introduction of bans on the use of PCP and certain pesticides has led to a significant improvement. However, the problem still exists.

Water usage for these processes varies considerably. Typical values are 10 to 20 litres of water per kg of scoured wool, and 10 to 30 litres per kg of scoured cotton.

Bleaching
This process is used predominantly on cotton or cotton blend fabrics or yarn, although it may also be required on wool and acrylic where a white yarn is needed. The whiteness of the goods (cotton or linen) is improved by treating with hypochlorite or peroxide. Nowadays, it is predominantly the latter that is used, at least for cotton goods. Hypochlorite bleaching can cause environmental problems due to the presence of chlorine breakdown products, but it still is the preferred method when bleaching linen goods due to the better level of whiteness that can be achieved. Absorbable organo-halogens (AOX) which are produced by hypochlorite bleaching, amongst other processes, are consented for discharge in some European countries. Notably, Sweden and Germany.
Desizing, scouring and bleaching, or more commonly just scouring and bleaching can also be achieved in a single continuous process. Washing ranges associated with continuous preparation invariably have countercurrent flow, lidded tanks and heat recovery systems to help minimise water and energy usage.

Principal pollutants: Effluent pH, residual chlorinated organics (AOX) and chemical oxygen demand (COD).

Effluent from bleaching operations contain the residues of oxidising agents, as well as alkalis or acids. Residual peroxide is not a problem, but other oxidising agents may reduce the effectiveness of some at effluent treatment plants.

Mercerising
This is the treatment of cotton or linen yarn or fabric with concentrated caustic alkali. It has the effect of swelling the fibres, increasing their strength and dye affinity and altering the lustre and handle of the material. Mercerisers are either chain or chainless and consist of three sections, impregnation, stabilisation and washing off.
Most mercerisation units have their own caustic recovery systems to help minimise waste.

Principal pollutants: Alkaline effluent from washing and rinsing operations.

Effluent from mercerising operations consists mainly of mildy caustic rinsewater. Typically the pH of this effluent is about 10 to 12. Water usage for this process is about 20 litres per kg of cloth.

The fabric, yarn or loose stock is now ready to receive colour. Dyestuffs can be applied by many different techniques to give shades which are fast to washing and light. Dyeing can be carried out at almost every stage of manufacture. Yarn dyeing is quite common, to obtain coloured yarns with which the weaver can produce a wide range of coloured striped or check designs for such fabrics as shirtings, bedding and dress materials.

TEXTILE COLORATION

Dyeing (includes: atmospheric, pressure and pad dyeing systems)
There are a wide range of machines and processes available for dyeing fibre, yarns, staple, tow, fabric and garments. Dyeing can be done continuously or batchwise, at pressure or in open vessels. The process chosen depends on the nature of the textile, the type of dyestuff and the end use.

Yarn dyeing is done at pressure on a package dyeing machine, with the cheeses or cones of yarn being mounted onto vertical hollow spindles. The spindles are lowered into the cylindrical vessel and the lid bolted down. Heat is applied via a steam coil and the dye liquor is forced through the package in a two-way flow pattern until the correct shade has been achieved. This is confirmed by testing a package held in a sample pot on the side of the main vessel. Liquor ratios vary from 3:1 to 10:1 depending on the nature of the dye and package .The liquor is then cooled using a heat exchanger before it is dropped to drain.

An alternative way of dyeing heavier yarns is the hank dyeing machine. Hanks of yarn are threaded onto horizontal poles and the poles are lowered into the dyebath. These machines tend to take up a lot of floorspace and are nowadays only used for dyeing bulky wool or acrylic yarns.

Machines used for dyeing loose stock are similar to those used for dyeing yarn except that the textile is placed in a basket or perforated cage instead of being placed on a spindle.

The continuous dyeing of yarns and tow is much less common. Machines are used for dyeing polyester and acrylic tow where the tow is padded through dye liquor and then through a tunnel for fixation and washing.

Fabric dyeing in batches is done on one of four basic types of machine. The jig, winch, beam or jet type. The jig is the oldest and simplest type of machine for dyeing woven fabric. It is suitable for fabrics which cannot be creased during processing. The fabric is wound on to a roll. This then passes through the dye liquor and onto a second roll. The process is repeated back and forth until the desired shade is achieved. These machines are very versatile and can also be used for the batchwise preparation of fabric (scouring and bleaching) prior to dyeing. Heating is through steam coils although direct steam injection is usually also provided for rapid heating up of the dye bath. The exhausted liquor is dropped hot directly to drain.

Jig Dyeing Machine

Winches are used for fabrics that can withstand creasing when in rope form. It is ideal for loosely woven cottons, woollens and some knitted and man-made materials. The fabric circulates, in a continuous rope of between 50 to 100 metres, over reels and rollers and down into a dyebath. Old winch dyebaths were constructed using wood, but these have been largely replaced with more versatile modern steel vessels.

Jigs and winches are atmospheric machines. There is a requirement however, for dyeing certain types of fabric at high temperature and pressure. These lightweight, delicate and knitted fabrics suffer creasing, damage and poor dye uptake on jigs and winches. The answer is to dye using a pressure beam or jet type machine.

Pressure beams consist of a roll of fabric wound around a perforated beam. This is placed in a horizontally orientated dyeing vessel and the door bolted shut. The liquor is heated using steam coils and circulated through the fabric. Dyeing temperatures are typically 120 to 130°C. On completion of the dye cycle the liquor is cooled using an integrated water cooling system. The warmed cooling water can then be stored at temperatures of about 40 to 50°C, as an alternative to passing it through a cooling tower, and used for subsequent dyeings.

The final class of machine used for batchwise dyeing of fabric is the jet or jet type machine. Fabric is circulated in a rope form with a vigorous circulation of liquor, at temperatures of between 120 to 130°C. Variations on this type of machine include fully flooded and Softflow machines useful for delicate and sensitive fabrics. As with the pressure beams these high temperature jets are fitted with cooling systems with the potential for reuse of the warmed water on the next dyeing cycle.

The continuous dyeing of fabric is preferred where large quantities of woven fabric have to be dyed one colour. It is therefore a more common process in American mills where orders tend to be much larger. The fabric is fed through a pad bath then nipped through rollers to remove excess liquor. It is then dried and the dye fixed. Fixation can be done at high temperature as with the Thermosol process for dyeing fabrics containing polyester, or it can be done using a steamer (saturated steam) as with the vat, sulphur and direct dyeing of cotton.

Principal pollutants: residual colour in effluent.

The pollutant load of discharged dye liquor is generally low, although reactive dyes still have relatively poor exhaustion rates. Where these dyes are used coloured effluent is still a problem.

Typical colour absorbances of reactive dye effluent over the visible range from 400nm to 700nm can be as high as 1 to 1.5AU (using a 10mm cell). This is considerably higher than consent levels, which can be as low as 0.01 to 0.06 AU for discharge to river.

Water usage in dyeing is relatively high since it not only includes the dye liquor, but also all the preparative, rinsing and finishing stages involved in the application of colour. Typically, from 4 to 50 litres of water is used to dye each kg of textile. This ratio is highly dependent on the type of dye machine, the fabric to be dyed and the class of dyestuff used to match the customer’s requirements.

In a typical process involving the pre-treatment, dyeing and rinsing of a cotton fabric a whole host of chemicals will be used. These include sequestrants, alkalis, bleaching agents, stabilisers, catalysts, crease resisting agents, acids, levelling agents, dyes, exhausting agents, soaping agents and softeners. Probably 20 to 30 chemicals, contained in 10 to 15 individual treatment baths/systems. The total effluent from these processes will have a COD of about 1000 to 1500 mg/l, a BOD of 300 to 500 mg/l, suspended solids of 200 to 400 mg/l, a pH of 6 to 8, a temperature of 35 to 45C and will probably also contain traces of heavy metals and PCP.

Printing (includes; rotary, flatscreen and transfer printing)
In rotary and flatscreen printing, colour is applied to a fabric by passing it under a series of rollers of screens where a part of the pattern is exposed, allowing the colour through to the fabric on the stroke of a squeegee. The printed fabric is then dried in an oven. In flat screen printing the colour passes through a screen onto the cloth, the pattern being produced by masking out parts of the screen. Each colour used in the design requires a separate screen. Well designed, mechanised flat bed machines give precise prints and are suitable for wide fabrics or large pattern repeats.

For roller, or rotary screen printing the required design is cut into the surface of copper rollers. Again, each colour in the pattern requires a separate roller. If a large pattern is used then the roller must have a bigger circumference. This is why large patterns are avoided in roller printing. By varying the depth of the engraving on the roller the shade depth can be altered. A characteristic of engraved roller printing is the sharpness of line and the very fine detail which can be obtained.

Rotary Screen Printing

Transfer printing differs from the other two methods in that the printed pattern is transferred from printed transfer paper onto the fabric by passing both over a heated roller.

The paper, which is printed with volatile dyes, is heated for 30 seconds at temperatures of up to 200°C. The dyestuff transfers to the textile by sublimation. The advantage of this type of printing is that no other chemicals are used and no other processes are required to finish the cloth. This helps to minimise energy and water usage. The quality of print however, does not tend to be as good as that achieved with flat screen or rotary printing.

Principal pollutants: colour in effluent from washing down. Low level VOC’s, formaldehyde and ammonia in fumes from the drying ovens.

After each printing run the rollers, squeegees, screens and print paste containers that have been used must be cleaned out thoroughly ready for the next print run. This is achieved using water spray guns and tub cleaning machines. Wherever possible water is recycled. However there is still a lot of water consumed by this process. For example, it takes 100 litres of water just to clean one screen or squeegee, and on average about 250 litres of water to process one kg of printed textile (transfer printing excluded).

TEXTILE FINISHING

Coating and Laminating
Coating processes were, in the past, large consumers of solvents. Solvent based coating formulations produced significant VOC (volatile organic compound) emissions. More recently, with increased environmental legislation, companies have gone over to water based, or low solvent formulations. Where alternatives are not available then recovery and abatement systems have had to be installed. Coatings are applied using a doctor blade on a roller, by padding techniques or by spraying. The textile is then air or oven dried and cured at a controlled rate.

Laminating, or the formation of a layered textile, is a common process used in the production of such items as internal trim panels for the automobile industry. Lamination can be achieved by either the use of solvent based formulations or hot-melt cured polyurethanes followed by low temperature curing through an oven, or by flame lamination where the component textiles are brought together and passed rapidly over a flame. This effectively seals the laminate.

Principal pollutants: Fume, volatile organic compounds (VOC’s), and isocyanates.

A wide range of solvent types are still used, although in much lower volumes, in coating and lamination processing. Where emissions exceed consent, which in the UK varies between 50mg/m³ and 150mg/m³ (as carbon), then process modification, such as solvent replacement or if this is not possible then some form of abatement is required. This can be done using carbon absorption or thermal oxidation/incineration, usually with heat recovery.

The formulations used in lamination and some coating processes commonly include isocyanate. The health implications of inhaling significant levels of this chemical are severe, and so strict limits are set on both workroom exposure and process emission concentrations to atmosphere.

Wet Chemical Finishing (includes; FR treatment, enzyme treatment, resin finishing, steam treatment)
A variety of finishes such as Proban and resin finishes can be applied by padding liquor onto the fabric prior to stenter drying/baking. The concentration of the liquor, the fabric speed and the moisture retention after mangling determines the level of pick-up on the fabric.

The application of an easy-care finish is one such process. Easy-care finishing reduces the tendency of the fabric to crease in wear and makes it much easier to iron after laundering. The same finish also prevents shrinkage during washing. These types of finish have greatly reduced the maintenance which cotton in everyday use requires, and have increased its suitability for apparel of all types.

Principal pollutants: Formaldehyde and ammonia emissions from curing processes.

Formaldehyde concentrations during resin curing processes are typically 5 to 15 mg/ m³ in the process emissions from the stenter and 0.2 to 0.5 mg/m³ in the workroom . Ammonia concentrations during ammonia curing of cotton fabrics can result in process emissions of the order of 4000 mg/m³. It is essential therefore that some form of abatement, such as a wet scrubber, is fitted to this process so that emissions can comply with legal requirements.

Mechanical Finishing (includes; raising, shearing, calendaring, schreinering and sanforising)

Mechanical finishing involves the modification of the fabric by means of mechanical action. Raising is achieved by passing a fabric over a series of wire rollers. This has the effect of pulling the surface fibres to give a brushed or raised effect. Shearing is almost the opposite, where protruding fibres are removed from the surface of a fabric by cropping the surface.

A calendar or schreiner consists of two heated rollers through which the fabric is passed. This has the effect of smoothing and flattening the surface, conferring a glaze, lustre or pattern on the fabric.

Sanforising is the shrinkage of cotton fabric, and is achieved by controlled dampening and drying of the relaxed fabric to remove any tensions and distortions which have appeared as a result of earlier processing.

Principal pollutants: Dust from raising and shearing.

Dust levels found near raising machines are usually in the range from 1 to 3 mg/m³, whilst near shearing machines they reach about half of this level.

Fabric Finishing (includes; water extraction, drying, pulling to width and heat setting)
After preparation, washing or colouration, textiles require drying. This is usually carried out in two stages. The first stage is mechanical dewatering using centrifuges, mangles and vacuum slots. Mangling is the most cost effective way of removing water mechanically but water retention levels are still quite high. Centrifuging can only be used for relatively small batches of fabric. It is more effective than mangling but costs almost twice as much in terms of the energy required per kg of water removed. It is a method more commonly associated with the woollen industry. Suction or vacuum slots are the most effective way of mechanical dewatering (except for woollen fabrics where water removal under suction is poor) but they are the most expensive. Improved drying rates alone may not be sufficient to justify the expense. An alternative use of vacuum slots is the recovery of chemicals from pad finishing operations. It is sometimes the case that they are bought for the chemical savings alone.

The second stage involves heating the textile and removing the remaining water by evaporation. This is done using cylinder dryers, stenters, batch drying ovens, infra-red or RF dryers.

The traditional way of drying yarn or loose stock textiles was by a warm air drying oven. A large batch drying oven which when full takes up to 24 hours to dry the textile load. More recently, radio-frequency (RF) drying has become widely used, as it produces a rapid and uniform drying of the textile goods, even though it is a relatively expensive process.

The latest RF drying systems use a combined vacuum arrangement and RF drying capability, enabling drying to be achieved at much lower temperatures. This helps to save energy and improve product quality.

Diagram of a Stenter

Fabric drying is usually carried out on either drying cylinders (intermediate drying) or on stenters (final drying). Drying cylinders are basically a series of steam heated drums over which the fabric passes. It has the drawback of pulling the fabric and effectively reducing its width. For this reason it tends to be used for intermediate drying. The stenter is a gas fired oven, with the fabric passing through on a chain drive, held in place by either clips or pins. Air is circulated above and below the fabric, before being exhausted to atmosphere. As well as for drying processes, the stenter is used for pulling fabric to width, chemical finishing and heat setting and curing. It is a very versatile piece of equipment.

Modern stenters are designed with improved air circulation, which helps to improve drying performance, and with integrated heat recovery and environmental abatement systems.

Infra-red drying is used for both curing and drying. It is used as either a stand alone piece of equipment, or as a pre-dryer to increase drying rates and hence fabric speed through a stenter.

In the carpet industry there are a number of different types of drying/curing machine used. Wool wash dryers at the end of scouring machines for drying the loose stock wool; wool drying ranges for drying wool hanks prior to weaving; and wide 4 and 5-metre latexing or backing machines used to apply and dry/cure the latex backing on to carpets. Low level VOC emissions are produced by this process.

Principal pollutants: Oily fume during setting of man-made fabrics/yarns.

Typically the setting of a man-made fabric on a stenter produces oil mist/fume emissions in the exhaust ducts at concentrations ranging from 20 to 200 mg/m³, whilst in the workroom levels may reach 10 to 20 mg/m³.

Stenter manufacturers now make abatement systems that can be bought with a new machine or retro-fitted to an old one, these systems usually comprise of a heat recovery section followed by an electrostatic precipitator. Provided the unit is cleaned on a regular basis then removal efficiencies can be as high as 85%. More simple heat recovery and filtration systems are also available, these tend to be cheaper but they require more maintenance than those based on electrostatic precipitators.

Garment or Product Making-up
The final production process, at least in the garment or domestic textile sectors, is the cutting up and sewing of the fabric. Cutting up is achieved by placing layers of the same fabric on a long table, and then automatically cutting through all the layers using a computer controlled system capable of organising the patterns so that there is minimal fabric loss. The sections are

then sewn up on industrial sewing machines. Where required the final product may be pressed or ironed or passed through a garment finishing oven before being packaged for final delivery.

Principal pollutants: Dust and noise from cutting up and sewing operations and residual formaldehyde from garment finishing ovens.

The noise from sewing machines can be quite high, especially when there are forty or fifty machines all operating in close proximity. As is usually the case. Levels have been recorded in the range from 80 to 85 dB(A).

Dust is also produced around a sewing machine by the action of the needle on the fabric. It of course depends on the nature of the textile, but again levels have been recorded as high as 5 – 10 mg/m³. More typically levels are in the region of 1 - 3 mg/m³.

Formaldehyde can also be a problem in some cutting and sewing rooms, where resin treated cotton or polyester/cotton fabrics are being used, especially around garment finishing ovens.

Inspection and Quality Control
Inspection and quality control is probably the only relatively clean stage, in terms of environmental pollution, of the whole textile chain. It plays an important role however, in terms of helping to reduce waste (seconds are sold on at much lower cost and so need to be eliminated) both of the product and of the raw materials, and to improve the quality of the product. The garment or item produced must wear well, must not contain any banned chemicals and must not affect the wearer or user in any way that may be detrimental to health.

Certain dyestuffs are known to trigger dermatitis, whilst formaldehyde is a well known irritant. It is therefore important to keep monitoring the processes in the textile chain and to test samples periodically to ensure that they comply with any quality or environmental standards.

Principal pollutants: none.

Recent Developments

There is always a trend towards increased automation, control and speed, and a reduction in labour and manual intervention. Most developments in textile machinery tend to be in this direction. Here are just a few of the more recent developments and trends, which will help to reduce the overall environmental impact of the textile industry.
Spinning: Recent developments include improved mini-carding sets to help provide more flexibility at lower cost, and carding machines designed specifically for re-cycled fibres. There are also more cutting, pulling and opening machines available, with a wider range of uses. For example in the recycling of carpet waste.
Machinery for the moth proofing of woollen yarn has also been improved so that much less liquor is used and wasted. Instead of using 1000’s of litres at a time these machines use only 10’s of litres, and virtually all of it ends up on the yarn.
Weaving: The on-loom automatic inspection of fabric enables faults to be detected immediately and so helps to minimise waste. Quick style change systems are also more in evidence, providing greater flexibility in product design.
The ordering of spare parts via the Internet has also just been introduced by some machinery manufacturers.
Reduced air consumption, energy and noise on air jet looms and lower weft waste on rapier looms are two more examples of recent improvements which could have an effect on the environmental impact of weaving. Highly productive multi-phase weaving machines, with very low noise production and energy usage, is also another development worth mentioning.
Knitting: Multi-effect garments can now be more easily produced, with the introduction of automatic needle changing. This should replace the slower manual cam changing required on conventional machines. Reduced noise, raschel and tricot knitting machines have also been developed.
Pretreatment: New developments here include turbo-rollers for increasing penetration through fabrics during preparation and washing. Liquor passes through a perforated outer shell with an inner fluted roller. Another development is hot steam washing which helps to remove contaminants more rapidly than conventional washing. There are even new designs in circular singeing machines to improve the quality of tubular knitted fabric preparation.
For wool scouring, high solids or dyehouse effluent, evaporative treatment followed by a secondary polishing stage such as reverse osmosis are becoming an option for those wishing to recycle virtually all of their process water. Recycling rates of up to 99.5% have been achieved by some wool scouring units.
Dyeing and Printing: In dyeing, or at least drying after yarn/loose stock dyeing, there are more developments in combined RF and hot air drying machines. These help to improve the speed and uniformity of drying.
There is also a move towards integrated dyeing/heat recovery systems, which use less water and energy and help to reduce dye cycle times. Pump powered fill and drain mechanisms, reel-less jet dyeing machines and jigs with built in padder mangles, low liquor usage, additional spray bars and vacuum slots for more effective dyeing and rinsing are now becoming options to consider.
Fully automated yarn and package dyeing plants, which monitor and control the use of water and energy have also recently been introduced.
In printing there is more of an emphasis on improving productivity with digital processing of designs and digital printing being the next major goal.
Finishing: Stenters are now sold with heat recovery and abatement systems as part of a complete package. Revolutionary stenter air circulation systems are also coming on to the market to help reduce the overall energy use in fabric drying. RF and air/vacuum dryers which allow drying to take place at only 60ÚC, produce significant energy savings for the drying of packages and hanks.
Steam agers are also now available with non-uniform steam concentration (low at the front and high at the back), which saves up to 30% on steam consumption.
Improved bearing systems, to help reduce energy usage, together with more efficient dust removal have helped to reduce the environmental impact of raising.

Reference WebSite: http://www.e4s.org.uk/textilesonline/index.htm

Ginning
From the field, seed cotton moves to nearby gins for separation of lint and seed. The cotton first goes through dryers to reduce moisture content and then through cleaning equipment to remove foreign matter. These operations facilitate processing and improve fiber quality. The cotton is then air conveyed to gin stands where revolving circular saws pull the lint through closely spaced ribs that prevent the seed from passing through. The lint is removed from the saw teeth by air blasts or rotating brushes, and then compressed into bales weighing approximately 500 pounds. Cotton is then moved to a warehouse for storage until it is shipped to a textile mill for use.A typical gin will process about 12 bales per hour, while some of today’s more modern gins may process as many as 60 bales an hour.

Yarn Production
Modernization efforts have brought major changes to the U.S. textile industry. Equipment has been streamlined and many operations have been fully automated with computers. Machine speeds have greatly increased.
At most mills the opening of cotton bales is fully automated.

Lint from several bales is mixed and blended together to provide a uniform blend of fiber properties. To ensure that the new high-speed automated feeding equipment performs at peak efficiency and that fiber properties are consistent, computers group the bales for production/feeding according to fiber properties.

The blended lint is blown by air from the feeder through chutes to cleaning and carding machines that separate and align the fibers into a thin web. Carding machines can process cotton in excess of 100 pounds per hour. The web of fibers at the front of the card is then drawn through a funnel-shaped device called a trumpet, providing a soft, rope-like strand called a sliver (pronounced SLY-ver).

As many as eight strands of sliver are blended together in the drawing process. Drawing speeds have increased tremendously over the past few years and now can exceed 1,500 feet per minute.

Roving frames draw or draft the slivers out even more thinly and add a gentle twist as the first step in ring spinning of yarn.

Ring spinning machines further draw the roving and add twist making it tighter and thinner until it reaches the yarn thickness or “count” needed for weaving or knitting fabric. The yarns can be twisted many times per inch.

Ring spinning frames continue to play a role in this country, but open-end spinning, with rotors that can spin five to six times as fast as a ring spinning machine, are becoming more widespread. In open-end spinning, yarn is produced directly from sliver. The roving process is eliminated.

Other spinning systems have also eliminated the need for roving, as well as addressing the key limitation of both ring and open-end spinning, which is mechanical twisting. These systems, air jet and Vortex, use compressed air currents to stabilize the yarn. By removing the mechanical twisting methods, air jet and Vortex are faster and more productive than any other short-staple spinning system.

After spinning, the yarns are tightly wound around bobbins or tubes and are ready for fabric forming. Ply yarns are two or more single yarns twisted together. Cord is plied yarn twisted together.

Fabric Manufacturing

Cotton fabric manufacturing starts with the preparation of the yarn for weaving or knitting. Annually, textile mills in the U.S. normally produce about eight billion square yards each of woven and three billion square yards of knitted cotton goods.

Woven Fabrics
Weaving is the oldest method of making yarn into fabric. While modern methods are more complex and much faster, the basic principle of interlacing yarns remains unchanged.
On the loom, lengthwise yarns called the warp form the skeleton of the fabric. They usually require a higher degree of twist than the filling yarns that are interlaced widthwise.
Traditionally, cloth was woven by a wooden shuttle that moved horizontally back and forth across the loom, interlacing the filling yarn with the horizontally, lengthwise warp yarn. Modern mills use high-speed shuttleless weaving machines that perform at incredible rates and produce an endless variety of fabrics. Some carry the filling yarns across the loom at rates in excess of 2,000 meters per minute.
The rapier-type weaving machines have metal arms or rapiers that pick up the filling thread and carry it halfway across the loom where another rapier picks it up and pulls it the rest of the way. Other types employ small projectiles that pick up the filling thread and carry it all the way across the loom. Still other types employ compressed air to insert the filling yarn across the warp. In addition to speed and versatility, another advantage of these modern weaving machines is their relatively quiet operation.
There are three basic weaves with numerous variations, and cotton can be used in all of them. The plain weave, in which the filling is alternately passed over one warp yarn and under the next, is used for gingham, percales, chambray, batistes and many other fabrics.
The twill weave, in which the yarns are interlaced to form diagonal ridges across the fabric, is used for sturdy fabrics like denim, gabardine, herringbone and ticking.
The satin weave, the least common of the three, produces a smooth fabric with high sheen. Used for cotton sateen, it is produced with fewer yarn interlacings and with either the warp or filling yarns dominating the “face” of the cloth.
In some plants, optical scanners continuously monitor fabric production looking for flaws as the cloth emerges from the weave machine. When imperfections appear, computers immediately print out the location of the flaw so that it can be removed later during fabric inspection.

Knitted Fabrics
Knitting is a method of constructing fabric by using a series of needles to interlock loops of yarn.
Lengthwise rows of these loops, comparable to the warp yarn in woven goods, are called wales. Crosswise rows, comparable to filling yarns, are known as courses.
There are numerous similarities in knitting done by hand and machine, but there are also some marked differences.
Most cotton is knit on circular machines which have needles fixed to the rim of a rotating cylinder. As the cylinder turns, the needles work their way from stitch to stitch producing a tubular fabric. Its width is regulated by the size of the cylinder, which usually ranges from 9 to 60 inches in diameter.
A hand knitter uses two needles forming one stitch at a time.
Depending on the width of fabric desired, a modern knitting machine might use over 2,500 needles.
Instead of a single cone of yarn, a knitting machine may have up to four cones per inch of fabric width. For example, a machine with a 32-inch cylinder can have over 2,700 needles and 128 cones of yarn feeding simultaneously. These are typical statistics for a machine used in making underwear knits, but figures vary according to the type of machine used and the fabrics produced.
The flat knitting machine is another basic type. Designed with a flat bed, it has dozens of needles arranged in a straight line and produces a knit fabric that is flat, similar to woven fabric.
A flat knitting machine makes over one million stitches a minute, and can be set to drop or add stitches automatically in order to narrow or widen the fabric at certain points to conform to specific shapes.
Knitting machines can be programmed to produce a wide variety of fabrics and shapes.

Cotton Fabrics
Cotton fabrics, as they come from the loom in their rough, unfinished stages, are known as greige goods. Most undergo various finishing processes to meet specific end-use requirements.
Some mills, in addition to spinning and weaving, also dye or print their fabrics and finish them. Others sell greige goods to converters who have the cloth finished in independent plants.
Finishing processes are numerous and complex, reflecting today’s tremendous range and combination of colors, textures and special qualities.
In its simplest form, finishing includes cleaning and preparing the cloth, dyeing or printing it and then treating it to enhance performance characteristics.
To produce a smooth surface in preparation for dyeing and finishing, the greige goods are passed rapidly over gas-fired jets or heated copper plates to singe off lint and loose threads.
Moving at speeds that can be greater than 200 yards a minute, the material is scoured and bleached in a continuous process that involves the use of hydrogen peroxide. The time for the chemicals to do the preparation reactions occurs from piling the fabric on conveyor belts that pass through steaming chambers, or stacking in large steam-heated, J-shaped boxes before the goods are withdrawn from the bottom.
If a more lustrous cloth is desired, the goods are immersed under tension in a caustic soda solution and then later neutralized. The process, called mercerizing, causes the fiber to swell permanently. This gives the fabric a silken sheen, improves its strength and increases its affinity for dye. Mercerizing also can be done at the yarn stage.

Dyeing
The most commonly used processes for imparting color to cotton are piece dyeing and yarn dyeing.
In piece dyeing, which is used primarily for fabrics that are to be a solid color, a continuous length of dry cloth is passed full-width through a trough of hot dye solution. The cloth then goes between padded rollers that squeeze in the color evenly and removes the excess liquid. In one variation of this basic method, the fabric, in a rope-like coil, is processed on a reel that passes in and out of a dye beck or vat.
Yarn dyeing, which occurs before the cloth is woven or knitted, is used to produce gingham checks, plaids, woven stripes and other special effects. Blue dyed warp yarns, for example, are combined with white filling yarns in denim construction.
One of the most commonly used yarn dyeing methods is package dyeing. In this system, yarn is wound on perforated cylinders or packages and placed on vertical spindles in a round dyeing machine.
Dye solution is forced alternately from the outside of the packages inward and from the inside out under pressure.
Computers are used increasingly in dyeing processes to formulate and match colors with greater speed and accuracy.

Printing
Printing colored designs on cotton cloth is similar to printing on paper.
Long runs of the same fabric design are produced on a roller print machine operating at speeds between 50 to 100 yards a minute. As many as of 10 different colors can be printed in one continuous operation.
A typical printing machine has a large padded drum or cylinder, which is surrounded by a series of copper rollers, each with its own dye trough and doctor blade that scrapes away excess dye. The number of rollers varies according to the fabric design, since each color in the design is etched on a separate roller. As the cloth moves between the rotating drum and rollers under great pressure, it picks up color from the engraved area of each roller in sequence. The printed cloth is dried immediately and conveyed to an oven that sets the dye.
Automatic screen-printing is another principal method for imparting colored designs to cotton fabrics. Although slower than roller printing, it has the advantage of producing much larger and more intricate designs, elaborate shadings and various handcrafted effects.
In flat bed screen-printing, the fabric design is reproduced on fine mesh screens, one for each color. On each screen, the areas in the design that are not to be penetrated by the dye are covered with lacquer or some other dye-resistant coating. The screens are coated with dye on the back and mounted in the proper sequence above a flat bed. As a belt carries the fabric along from screen to screen, a squeegee or roller presses the dye through the open area of the screen onto the fabric.
The new flat bed machines can have speeds of up to 1,200 yards per hour for a fabric with a 36-inch design repeat.
Faster by far are the recently developed rotary screen printing machines with production speeds of up to 3,500 yards an hour. The system combines roller and screen printing, utilizing perforated cylinders instead of flat screens. The color paste is fed inside the cylinders and a small metal roller forces the color through the pores of the cylinder onto the fabric which is moving continuously under the cylinders. As many as 16 colors can be printed on one fabric using this method. Use of this technique is increasing since the screens or cylinders can be produced less expensively than the engraved copper rollers used in roller printing.

Finishing
Finishing, as the term implies, is the final step in fabric production. Hundreds of finishes can be applied to textiles, and the methods of application are as varied as the finishes.
Cotton fabrics are probably finished in more different ways than any other type of fabrics. Some finishes change the look and feel of the cotton fabric, while others add special characteristics such as durable press, water repellency, flame resistance, shrinkage control and others. Several different finishes may be applied to a single fabric.

Reference WebSite: http://www.cotton.org